The present invention relates generally to a measuring apparatus, and more particularly to a measuring apparatus of an incident angular distribution or a light distribution characteristic (also called “an effective light source” and “a σ distribution”) on an illuminated plane. Here, a measurement of an effective light source distribution of an illumination optical system intends to cover not only a measurement of the σ distribution, but also a measurement of the centroid (or center of gravity) of illumination light.
A projection exposure apparatus, which is conventionally used for the photolithography technique to manufacture fine semiconductor devices, projects a circuit pattern of a reticle (mask) onto a wafer, and the like, via a projection optical system, thus transferring the circuit pattern.
Along with the recent demand for finer and lower profile electronic devices, finer semiconductor devices mounted on these electronic devices are increasingly demanded. A higher quality exposure requires an effective light source optimal to a reticle pattern. An effective light source distribution depends upon an adjustment of a light intensity distribution near an exit plane of, e.g., a fly-eye lens to a desired shape, such as a normal illumination shape, an annular illumination shape, and a quadrupole illumination shape. Moreover, a projection exposure apparatus is demanded to control its numerical aperture (“NA”), coherence factor σ (which is an NA of an illumination optical system/an NA of a projection optical system), and an effective light source, thus setting up a condition optimal to each of various characteristics.
Control over the coherence factor σ needs a more accurate measurement of an effective light source distribution. A measurement of a light intensity distribution on an incident pupil plane of a lens will provides the effective light source distribution. The measurement of the effective light source distribution also provides a measurement of the centroid of illumination light on the incident pupil plane, which causes an asymmetry of the imaging performance, i.e., the so-called telecentricity.
The conventional method of measuring the light intensity distribution on the pupil plane is seen, for example, in Japanese Patent No. 2,928,277, Japanese Patent Applications, Publication Nos. 2000-19012, 5-74687, and 2002-110540.
These conventional measurement methods require, in addition to a reticle, etc., a measuring apparatus, such as a mirror, a condenser optical system, a relaying optical system, an image sensor, and the like, to be arranged on a plane or planes conjugate with reticle and wafer planes. However, an accommodation of these components in an exposure apparatus would increase the cost due to its limited capacity. In addition, such measurement methods should be applicable to an immersion exposure apparatus.